take this with some reservation because I've not used business model canvas extensively. my understanding is that business model canvas gives you an overall shared understanding of a long-term vision, with some idea around your key stakeholders, partners and activities. from that canvas, you should be able to identify some key assumptions to validate, and key initial milestones. each of those initial milestones would then potentially become a center of an impact map, where you can detail how it leads to deliverables, and list impacts that would lead to that outcome.
so if you want to combine them, i'd suggest doing the business model canvas first, figuring out the next milestone (3-6 months) from that canvas, and then mapping it out.