Based on some of my readings he did a stint in the U.S. Army Special Forces. Can you guys help me confirm this? Thanks!

His nationality seems to have changed a few times. Most of the early stuff seemed to indicate he was an American who joined the Canadian Military for Department K, who drafted him into Weapon X, but then the more recent stuff makes him out to be a Canadian born and bred. I think he was always in the Canadian military though- was the series you read the Marvel Knights 'Wade Wilsons War'? Because that's not canon...
 
EDIT: Here's some pages from the old Deadpool & Death 1998 Annual, pretty much the first attempt to show his Weapon X days. Kind of suggests he didn't join the military at all here, just the program... But I know the whole thing got fleshed out more later.

i always thought that he was a Canadian who joined the U.S. Army then was kicked-out then turned Mercenary then Weapon X subject then turned costumed mercenary...

Here's how I think it worked. 
 
1) He was born in Canada by his mom and dad. 
2) His dead left and his mom became an alcoholic. 
3) His mom moved to the states and remarried to a US army General. 
4) His mom died of cancer and he was left with his abusive adoptive father.
5) His father was shot by one of his friends in a bar fight and Wade left and joined the USA military.  
6) At some point he dropped the USA military and became a mercenary, working on a secret government hit squad (with members like Slayback, and Garrison Kaine.)
7) Wade then got into trouble with T-Ray and he either stole T-Ray's identity or T-Ray stole his. (It depends on the writer, but personally I think Deadpool is the true Wade Wilson)
8) Wade discovers he has cancer
9) Wade is told by Garrison Kane about Department K, and how they could cure his cancer.
10) Wade was experimented on and became a failed experiment.
11) The rest is self explanatory.
 
He's Canadian but worked for the US army, it's the only way the two possible origin stories he has could work.

It's a crapshoot.
 
Nicezia pretty much left it up in the air (but he himself said he was US born, joined the military), etc. 
 
The only stuff we've seen on panel however, is DP was a merc, and a damn good one at that in DP -1 when he was being considred for the Mithras Project the first time around. Then he averted a catastrophe (the murder of Copycat) only to get cancer. Then we know he had multiple attempts to treat it. He somehow met Garrison Kane and was given the idea to check out Department K/Weapon X. The rest is pretty much common knowledge.
 
Of course Daniel Way ignores ALL of this except 'military, cancer, weapon x" and no particular order, rhyme or reason. Thanks for not doing research Way! The casual fans know more about the character you've been writing for years now!

  The Lobster  i totally buy this...  
 i just cant pinpoint where Dp, got all his fighting skills from?? anyone>>? 

"Of course Daniel Way ignores ALL of this except 'military, cancer, weapon x" and no particular order, rhyme or reason. Thanks for not doing research Way! The casual fans know more about the character you've been writing for years now! "