Traveling from the U.S. to New Brunswick, Canada?

Alright, so, I'm planning a trip from Nevada to preferably Fredericton, NB. I have to travel by land, because I have a passport card. I was wondering what the cheapest way to do this would be. I don't have a car, so driving myself isn't an option. If I were to take a bus to Houlton, ME, a friend of mine can likely pick me up once I'm across the border, but I'm not sure if I'll be allowed to just walk across it, or if I'll have to take a shuttle of some sort... Any help?