I share your concerns and am glad that there is now a group for this. I think people might be more liable to donate if in addition to general donations, you had a goal to build an underpass or an overpass every year, with specific funds going to this. Even if it started out with a simple underpass for frog and toad hatches, it could evolve into something bigger and expand to all provinces.
I don't think telling driver's to watch for wildlife is going to have a huge impact as in today's world most people speed (unfortunately it's the way of today's life). If animals have a safe corridor they will hopefully use it. The government should be on board with this as this has been successful where they have implemented highway underpasses. I would be happy to start the donations with $100 if you did this.