When your buddy keeps saying he's got a girlfriend, but you never meet her, then he probably has a "Canadian girlfriend". It can also be understood as imaginary girlfriend.

如果你的哥们总是说他有女友，你却从没见过，那么他那位很可能是“加拿大女友”。也就是想象出来的女友。

Example:

Vince: "Trevor, why haven't we met your girlfriend? You've been dating for over a year."

Trevor: "She's really busy."

Vince: "Oh, yeah, I forgot how busy Canadians can be."

Trevor: "What?"

Mike: "Vince is just saying you've got a Canadian girlfriend, that's all."

温斯：特雷沃，为什么我们总见不到你的女友？你不是约会了一年多了嘛。

特雷沃：她真的很忙耶。

温斯：哦，对对，我忘了加拿大人真的很忙。

特雷沃：什么意思？

麦克：温斯的意思是你交的是“加拿大女友”，你自己想象出来的，其实根本不存在。