dantambok
TPF Noob!
I just want to ask.. Whats the appropriate largest print i can make from a 7D?

Thank you very much for that. Btw, what is upscaling?Doesnt really matter.. Its all about where you look at it. A billboard is seen very far away. I bet you if you climb the billboard and look at it very close, it is very pixelated and ugly.
Your 7d has 5184 x 3456 pixels. For best quality print (to be viewed closely), you want between 250 to 300 dpi. So I would say it is about 5184/250 = 20 in wide.
If you dont care about the quality and go for a poster quality you can divide it buy maybe around 150dpi = 5185/150 = 34 in wide.