Hello everyone!
I just joined this forum after some much needed advice from anyone who has used either of these lenses, it would be greatly appreciated! Wildlife photography is new to me, so I apologise for any mistakes! 
A quick background: I am traveling out to British Columbia in Canada for two years on a working holiday visa (I'm 22). I'm then heading up to the beautiful Yukon! I currently take landscapes with my Canon 17-40mm f/4L but would love to capture the wildlife in Canada whilst I am there. (Bears, eagles, moose). I also have a 24-70mm 2.8 lens which covers a lot of needs for me.
I have read so much about the prime Canon 300mm, newer 70-300mm and also the older 100-400mm f/4.5-5.6L- but still cannot make up my mind! My budget is around £1000, I am looking to purchase second hand. Weight and size is a factor, as I am traveling around the country/staying in hostels etc.
I understand that the 70-300mm is incredibly sharp, compact and weather sealed, but I worry that I would feel that 300mm just isn't enough for some of the wildlife I would see in Canada, and no teleconverters can be used on it? I also don't think I would use any other length other than the 300mm on this lens.
I am leaning slightly more towards the 300mm prime, as I have the option of adding the teleconverter and I have read great reviews of this combination. The older 100-400mm model worries me as I have read a few negative reviews regarding the image quality and of course, its age.
Anyway before I drive myself absolutely mad ...some advice on which telephoto to buy would be amazing!!






