We are going back to BC next summer. You could (we will be) spending at least 6 weeks just in BC, and the Alberta Rockies. We do not know a lot about central Canada, but the East coast is worth a visit. We haven't hired a van there, yet, but hope to do so sometime - Nova Scotia, Prince Edward Island & Newfoundland. Have you thought of doing it in two stages and fly between West and East coasts?
We had an amazing week in May last year - a weeks hire from Calgary. Went up to Jasper on the Icefields Parkway, and was just what was needed after sorting things out in Vancouver after Neil's accident. Do not miss that. The previous September we had driven across BC from Vancouver to the Rockies, and back, in 3 weeks, which was not nearly long enough, which is why we have planned another trip.
Happy to answer any specific questions, if I can.
All the best to you both, and safe travels