You have to walk a loooong way from the aircraft to immigration. If you're lucky the new high speed moving sidewalk will be running which is apparently quite a ride. But it's been shut whenever I've been there.

I've never been there at 6am so I can't say if the lines for immigration will be long or not -- I'm guessing not. It's usually pretty quick in my experience. Then you have to wait for your bags -- pick them up right away because those carousels are murder on bags.

Then you walk through customs and hand in your paper and normally drop your bag right back on the carousel on the other side. They're checked through anyways so there's no processing for them. You can walk out with them but then I don't know what you do to check them in. I suppose you go to the regular checkin desk.Then you follow the signs to transfers which is another long walk, go back in through security, and you're in the domestic departure terminal with plenty of cafes and stuff.

You might check whether there's a servisair lounge you can pay for access at, it's probably worth it for such a long stay though in my recollection they have a 3 hour maximum. Or better yet, beg on the Air Canada Aeroplan forum for lounge access -- some FF might take pity on you. I don't remember if they have to be on the same flight as you or not but there's a decent chance someone might be.

Actually if I recall correctly you can buy access to the Air Canada domestic lounges anyways. You might check into that.