Occams razor demands the simplest explanation. If there really is a 10ft primate in North America, it's more likely to be a species that we know existed but thought was extinct.
Gigantopithecus blacki went extinct in China about 100kya, and is about the right size at 3m. It's not impossible that it survived later than thought and crossed the bearing land bridge, but there's no evidence of this. It also doesn't match up well with the bigfoot mythology, given that it was probably vegetarian and quadrupedal. It's also more closely related to orangutans than to humans or our closest cousins, chimps.
Another candidate would be homo erectus palaeojavanicus. These were a giant human species know from a few fossils found only on Java. They're closer to the bigfoot mythology, being bipedal and omnivorous. But it seems unlikely that they would have been able to maintain their size while they expanded through (presumably) interfertile h. erectus territory and ended up in NA. A good question at this point would be why h. e. palaeojavanicus crossed instead of the typical-sized h. erectus. (Not really looking for a PIDOOMA answer.)
The suggestion of aliens just needs so many more assumptions. That they exist, that they can travel faster than light or are billions of years ahead of us, that they have any interest in visiting and that they have any interest in visiting to leave behind hairy humanoids, that they have interest in concealing their presence and they're good enough to never leave any physical evidence despite sometimes landing on roads. And how they manage to be spotted so frequently but never photographed. Well, I guess that's the same assumption that we have to make with any bigfoot origin.
gosh, I'm astonished, your many words are, well, I'm a gr-8'er, I just don't understand what all ya said!

