Lens to use in Alaska

Planning a trip to Alaska next year. Would it be better to get a canon 300 f/4 + 1.4 TC
or the canon 100-400 f4.5-5.6. The lens will also be used for air shows.
What about dust infiltration into the lens and camera body due to push pull design.
Currently have a 10d 17-40 f4 and 70-200 f4

I think you will get a sharper image with the 300 f/4, but the 100-400 will be more versatile, the IS will be helpful too. If I were you, I think I would take the 100-400.

Yep. Get the 100-400. It'll be more flexible both there and at air shows. I doubt that the push-pull will suck any more dust past the lens' seals and gears than a normal "two-touch" zoom would as the lens groups are pushed back and forth. Whether it's one-touch or two touch, the lens groups will have to move around to focus and to zoom.