Anyone had experience with pets and layover flights or with Air Canada?

We found a great deal on flights from Dallas to Heathrow with a layover in Toronto. The cats will be flying into Toronto with us as access baggage, and then checked into cargo for our flight into Heathrow. We are a little worried if the four hour layover in Toronto will allows us enough time to check our two cats onto the connecting flight to Heathrow.

Has anyone had an experience with catching a connecting flight with their pets? Would we be picking out pets up at the baggage claim area? The cats are supposed to be checked in for the Toronto to Heathrow flight four hours before departure. If we are a little late to check in, will they deny the cats from boarding?

Also, any personal experiences with flying pets on Air Canada would be nice to hear.

I've used AC for internal and international flights with the cat, and they're good with animals.  Buy yourself something to eat, though...  and bring a warm coat.

For the other questions,  DEFRA and AC are the people to ask.  Maybe the Ministry of Agriculture in Canada.  I'm wondering if you'll need another vet check in TO, and whether they'll want an export fee.  Hopefully not!  Check to see how you pay for the cats flights.  I had to pay cash at the counter for Madeira's flight to Japan, AC didn't accept credit cards.  I was not prepared.. I thought I had already paid.