Interceptor or HeartGuard Plus are fine and have been on the market for years they are effective and easy to take along on road trips, especially if you are crossing the border.
When you take pup with you, check out the area before you let him do his business. If it looks like every dog on the road has used that areayou probably should take him to another spot.
Keeping stool picked up on your property will also help keep parasite infestations low.