It may be problematic.
Geez. I drove into Canada with my *very used* downhill skis, strapped to the roof. No problem.
Coming *back* into the US...all kinds of grief; US customs wanted to see my *bill of sales* for them ... Somehow, I talked my way out of having to declare them. So, I can’t imagine a *van full of dogs*.
With skis it's taxes...with dogs it would be rabies (and other diseases).