This board's clichè of the ARW patriots hating their fellow Canadian colonists' guts is besides way annoying, horrendously exaggerated.
1) There was a sizable Catholic minority within the 13 Colonies that enjoyed full civil and political rights political equality: there are signatures of Catholics on the Declaration of Independence and the Constitution. Conversely, there is not *one* documentary evidence of a significant political drive during the creation of the USA to deny Catholics full equality, either at the state or federal level. As for French language, back then it was the second language of culture for educated American elites. There is a distinct lack of Protestant mobs during the ARW howling for the blood of Catholics.
2) The leaders of the American Revolution were quite eager to bring Canada onboard, as proved by the invitation letters they sent to the Quebecois during the ARW, and the pre-approval for membership of Canada in the Articles of Confederation.
3) The one and only thing that the Patriots were (mightly) pissed off about the Quebec Act, is that by carving up the trans-Allegheny territory to Quebec, London was closing it off to settlers from the 13 colonies.
Would the presence of Canadian representatives at the Constititutional Convention made things a bit more complex ? Yes. But the reasonable concerns of the Quebecois for protection of their religion and language from federal interference were fairly easy to address in practice (it would not take more than a couple extra clausles in the Constitution that would actually cost the other states very little to write in) and otherwise, 1787 federalism already granted an overwhelming degree of autonomy to a community that was the majority in a state. As long as the Quebecois would not go out of their way to harass local Protestant or English-speaking minorities, widespread respect for states' rights would ensure Quebec a cozy place within the American system. Apart from cultural and religious peculiarities, the interests of Quebec would actually align with the ones of some among the other 13 states on most other issues. To settle the concerns of Quebecois about integration in the USA would actually be quite easy in comparison to the compromises that were necessary at the CC between small and large states, and between free and slaveowning states.