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Air Canada is one of the best airlines I have been on. I have Star Alliance Gold privileges, which means I have travelled on a lot of airlines, to a lot of destinations.
I often take 1DX, 1DIV, 70-200/2.8L IS II and five or six shorter (expensive) lenses on Air Canada. No problems. I recently purchased a TT Airport Commuter bag (see list below), which will take a 500/4L IS without camera or 300/2.8L IS with camera mounted. I'll be taking my 300/2.8L IS and shorter lenses to the US early next year. I don't know if you can wedge a 600/4L IS into the Commuter, but there are many other options that could do it. I've moved away from roller bags, as they often have to be checked in the smaller commuter airplanes operated by most airlines, including Air Canada, United, US Air, Delta and etc. I figure the Airport Commuter is small enough to stay in the cabin with me on almost any aircraft. I've been using the North Face Recon II daypack for this purpose for years, but it's just not well suited for camera access while you're actually shooting an event.
I try to stick to the 10kg weight per carry on bag. You can have a 'standard article' carry on and a 'personal article' carry on, giving a total of 20kg over two bags. As shown in the attached table, the 'personal article' bag can be substantial. I use a MEC shoulder bag that can easily hold a 1DX, 70-200/2.8L IS II, 24-70/2.8L II, 85/1.2L II and an X-Pro 1 system. I'll often load more than 10kg into the 'standard article' bag, as it has decent shoulder straps, but I can reload across the two bags to balance the load within the 10kg-per-bag limit, if I have to.
Some airlines, notably vacation charter airlines, have much more restrictive size and weight limits. Don't forget, no matter what the airline says on its web site or even in person at the start of the trip, the rules can change during transit, especially if there is a security scare. I was in Heathrow a few years ago when something was happening and they announced that only one small carry on article was allowed per person. If you couldn't live with that, you couldn't get on an airplane.