Absolutely not. In fact, just the opposite. Only same day itineraries with onward international [i.e. outside North America] space in F, C or J can get lounge access at intermediate and/or gateway airports. Otherwise one must have a membership in their particular lounge program, Priority Pass or similar credit card tie in with the airline being flown, or hold non-American top or mid-tier elite status in the appropriate alliance partner. In the case of UA, flights ex-Canada flights are permitted access to MLLs on the Canadian side since AC offers the same benefit to travellers in their front cabin, but you won't get access to a RCC from the American side into Canada unless you've got RCC membership or non-UA/US STARGold.

This was clarified when UA inadvertantly refused to even acknowledge AC STARGolds for RCC access when flying into Canada, or continuing onward within the USA.