Who is buying the tickets?

If Air Canada, will you be able to purchase the more expensive Flex class, or like many business travellers will you be forced to purchase cheaper Tango class tickets?

If Tango, I would avoid Air Canada and Air Canada's program. It will be very difficult to earn any status or perks.

As others have said, I would seriously look at United. They have a very good program and it's fairly easy to earn status.

(At least until United adds "Basic Economy" (BE) that route and if you're expected to book BE like some business travellers are being made to do.)