Air Canada Rouge, although owned by Air Canada, is not Air Canada. It is a budget airline with very tight seating. Check their planes on seatguru. I would not want to be shoehorned into their seats with below standard pitch for a transatlantic flight, and in fact friends of ours who never went to Europe before took a Viking River Cruise and let Viking get them the airfare. Outbound was Rouge, which they did then realize, and they reported being completely miserable.
Frankfurt through Lufthansa and Star Alliance should give you the necessary connections.