It might be cheaper to fly. Van rentals can be very expensive. Some companies will not allow you to take the vehicle across the border, others will charge a surcharge.
That's a VERY long drive, you also have to factor in the cost of extra hotel nights and meals. You can not safely make that trip without stopping for a sleep period (I don't mean grabbing a few zzz's in a rest area.) Depending on where you are in Canada, look into WestJet, they partner with JetBlue in the US, and I've seen some fairly attractive rates there.
Anne