Heya,
Depends on what you want to shoot. Really depends on what is even available to you when you want to shoot wildlife, because a big part of it is getting to know the wildlife (their habits, habitat, breeding season, location, migration, food source, water source, etc). That way you know what you'll even have a chance of seeing, and where, and when. It may also be worth mentioning, do you want your photos to represent the wildlife in their habitat, or do you want chance encounters (like images of birds on power lines or roof tops) and don't care if there's non-wild elements, like human occupation stuff involved. Some don't care. Some do. That's for you to decide.
A) Hiking. I've seen plenty of people with big lenses walking on common pathways in parks or areas and just go for chance encounters. Works ok with areas and species that are tolerant and not easily spooked. There's also hiking off into areas without people, where you're out of place, and easily spotted and spooking everything, which requires you combine hiking and chance with knowing about your target subjects and getting their earlier. So you can combine the two, or do them separately, etc. Depends on what you have access to, and time for. Not sure if hiking 10+ miles into a place to see a specific subject early before it will arrive is feasible in reality for you or not. Mean while, walking park pathways and seeing common subjects can be convenient and take less time, but may also be less rewarding after a while (personally I do not care to ever see a squirrel or gull).
B) Treating this like you're hunting will get you more shots on subjects that are harder to approach, and be able to do it in locations where you're out of place. Walking through the woods mid-day, you'll likely not see much, they hear you coming and smell you, and spook off before you even know it. Mean while, if you hiked out to a location with a hide, or just a good place to hunker down and not stand and be obvious and move around a lot, you may wait a while, but you'll then have opportunities to be closer to subjects that wouldn't let you get close and get them in their environment (especially things like King Fishers or Deer).
C) You can certainly combine the two. Depends on the outcome goals.
In Florida, I can drive around or walk pathways and easily see lots of birds and various wildlife. But, for the kind of shots I want, in the locations I want, a hide works best for me and I simply target the time, location and subject based on what I want, and set up before they're expected to be there. I also kayak waterways for another sneaky way to get close to birds & wildlife. Depends on how much time you have to put into it and what you want out of it.
I get so close these days, I don't even use my 600 hardly anymore. I more commonly shoot my 300 F4L IS more than anything for birds/wildlife, because I get close with hides and/or water way (kayak). I tired quickly of walking trails or common pathways and seeing the same subjects in less attractive locations. Sure, I can go see a hawk, osprey or wood stork in a local park virtually every day, but its an uncovered area, harsh light, everyone else is there, and I hate seeing power lines or power poles or man-made stuff along with them. Those opportunities are fun at first, with a long lens, but it wore off quick when I wanted images that showed the subject in their environment in good light. I had to plan and find those. That's where hides came in and stalking/kayaking.
I live near the west coast of Florida, so I sometimes combine the above, and simply drive the coast and walk to a few short to access areas where I know I'll always have a chance at some birds or local wildlife. Effortless really. I just go during the time of day I know they'll be active (incoming/outgoing tide mostly for many bird species). Near water, I'm always going to see a Heron, Egret, Eagle, Hawk or Osprey usually. I can literally just drive and point a lens out the wind. Or walk on the shoreline and see tons of birds of all varieties. It's not so easy for mammals though, like deer, where I need a blind and I need to be there before the sun comes up (hard to get out of bed sometimes!). Or if I want to see big reptiles like Gators, I know where/when to go and can basically go see one any day of the week. But again, there's a difference between the opportunity shots in bad light or a bad location, and planning ahead and getting the best light (waiting for the weather to be right) and going to locations where the environment is what you want in your shot.
When I don't feel like leaving my house, I have a feeder station that I keep stalked and a blind/hide, so that I can view/image song birds at close range (I can be within a few feet of them). I've even used lighting with it. But there are days I'm lazy and I just step outside, hang in my blind/hide, and the song birds do their thing on my feeders and I image them while they perch above the feeders waiting for their turn to get a bite.
Ex of one of my feeders, for my lazy days:

IMAGE LINK: https://flic.kr/p/T6yhTt
img_a1345_stitch
by
Martin Wise
, on Flickr
Ex of one of my portable blinds, for cooler days for spooky stuff:
IMAGE LINK: https://flic.kr/p/yG48LG
birdingblind_MKIV
by
Martin Wise
, on Flickr
When you're able to get within a few feet due to a hide/blind, you can get shots with 300mm or less and not have to crop much. Example at just 273mm:
IMAGE LINK: https://flic.kr/p/rqFnEt
IMG_3849
by
Martin Wise
, on Flickr
Here's 300mm in the rain, purposefully dragging shutter:
IMAGE LINK: https://flic.kr/p/Kvg6cN
IMG_2082
by
Martin Wise
, on Flickr
And here's 300mm with flash involved (I pre-setup a big 47" softbox near a perch):
IMAGE LINK: https://flic.kr/p/M47zrG
IMG_3537
by
Martin Wise
, on Flickr
Very best,