Replying to Camera advice: Sony a77 or Canon 5D mk2

I've been looking at getting a DSLR for a while (yes I'm aware the a77 is a DSLT but for now I'll just call it a DSLR) and was given some good advice at a local camera shop about what to go for. The guy in the shop said that for filming skiing and taking burst photos the a77 excels because of its weather-proofing and burst speed. All in all it is a great camera, but those two factors make it particularly tempting for me. On the other hand, a friend is looking to sell his Canon 5D mk2. Not sure of the price yet but it will obviously be cheaper. Other advantages of the Canon is that I don't have to buy company specific extra lenses further down the line. I'm no expert on filming, I really enjoy editing and skiing, so I really want to learn more but any advice you have would be awesome. I'll comment the price of the 5D when my friend messages me back. Thanks!