The 39-year-old actor posted a photo of himself with Connor and urged his fans to join him in donating money for the young boy's treatment cost, reported E! online.
"Ladies, gentlemen, boys and girls. This is my friend, Connor McGrath. He's quite possibly the biggest #Deadpool fan on earth. He was also the first person ever to see the Deadpool film.
Like Wade Wilson, Connor's trying to put cancer in his rear view mirror. About 6 weeks ago, I traveled to Edmonton Alberta to show Connor the movie at his hospital....Connor's the funniest, potty-mouthed Canadian mercenary I've ever met," Reynolds tweeted.
"He's my friend. I know lots of celebrities jump up and down touting a cause -- and maybe I'm no different. But holy frozen shit-slivers, I love this kid. He's the GREATEST. And he needs your help to get well. I've donated to help Connor and I hope you will too," he added.