Late autumn in Montreal and Quebec City is quiet, crisp, and noticeably cheaper once the foliage crowds head home. You get European bakeries, cobblestone streets, and cozy bistros without the summer prices or packed sidewalks.
A realistic budget for a solid four-day trip runs about $1900 for two people. Spreading that cost out lets you take the trip now without taking a sharp bite out of your checking account.
An intro window is a deadline, not free money. Pay at least $126.67 every month so the $1900 is completely gone before the 15 months end, or regular interest rates will apply to whatever is left.