US and Canada have similar immigration system. They treat non citizen the same way. Canadian as non citizen face the horror from us immigration system and American as non citizen face horror from canadian immigration system. The system base on anwering question to determine if you can get in. every visitor assume to be immigrate unless proof otherwise. every visitor have to be proof of non immigration intent. if your girl friend is reside other country , you will be assumed having immigration intent, if you do not have job, i will be assumed immigration intent.if two people travel together, your relationship will be investigated. if you travel alone, you will be ask why, your family status etc. depending IQ of immigration office, you will be ask strange question you can think about. american and canadian normally can only see half side of story.
my conclusion, you should not visit US and Canada for leisure purpose, if you are non citizen and you do not like to be asked such personal question.