Unfortunately, your Immigration Canada doesn't make allowances for your bf to be able to be "legal" in Canada just because you're very much in love and don't want to be separated anymore. Unless you are married, or you have lived together for at least one continuous year to establish a common-law partnership, he is not eligible for permanent residence as a "family member". He could apply in one of the other categories, such as a skilled worker or business entrepreuner, but family class, no.
If you are looking at getting married, then after you do you can apply to sponsor him for permanent residence in the family class. The
outland PR application forms you're looking at that say "from outside Canada" are the ones you should use - US citizens are seldom in a good position to apply for PR via the "inland" application process because US citizens are very often not given any documentation from CIC that proves when they entered Canada. This causes lots of complications with an inland application and can cause processing to be delayed for years! The "outland process" only means that the application is processed at the Consulate in Buffalo, NY instead of being processed entirely in Canada. That doesn't mean that your bf (future husband) has to be in the States. He can stay with you in Canada FOR AS LONG AS HE IS AUTHORIZED BY IMMIGRATION CANADA TO DO SO. Typically a US citizen who is admitted to Canada is authorized to stay for up to six months. If he stays longer than that without getting authorization from Immigration, he jeapordizes his PR application because he puts himself in the position of being subject to enforcement action for overstaying, and that could get him excluded from Canada. If he gets excluded, he won't be able to come back until the exclusion order is satisfied, even if he's awarded permanent residence in the meantime.
There is more information about sponsoring a US citizen spouse for permanent status at the
US2Canada website. I'd suggest you read through the info there, and then come back with any specific questions. There's a lot to this process, and once you understand how it works, you'll be better able to get the info you need.