What do you mean by "NE"? Like the northeast US? AC wouldn't be able to sell a connection from OKC to another Murrcan city connecting in YYZ, that is illegal and would be cabotage.
Definitely OKC-YYZ-Europe/India would be an intriguing option if AC ever took the plunge.
I'm not sure what your last bit about pre-clearance means? Preclearance is when you go through US customs/immigration in Canada prior to boarding your flight to the US, so you do go through US immigration, you just do it in the country of departure.
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