Quebec City in September is about crisp air, old stone walls, and wandering through Lower Town without dodging massive crowds. The summer rush has cleared out, the weather is still warm enough for a patio lunch, and you get to see the historic architecture at a slower pace.
A typical trip runs about $2000 for flights, a good hotel, and food. Spreading that cost out over time makes it easier to handle without draining your checking account all at once.
That 0% window is a deadline, not free money. If you still have a balance left when the 18 months are up, interest kicks in on whatever you owe.