Heart Murmurs aren't always you know, a death sentence or anything, but being that the pup was sold to you in that condition and they didn't mention anything about that means that pup has never been to a vet before. With an ethical breeder the pups will get checked out 2 or 3 times before they go to their new home... and 7 weeks is too young to be away from the family anyways. So all those things combined just leave me to believe you are in for a lifetime of problems with this guy.
I don't know of pet health insurance in Canada, but I have to reiterate to look into it. Make sure you get one that covers genetic problems & surgery, because if he is already limping he may need several surgeries when he is older. My rottie needed hip replacement and other surgeries and physical therapy. We spent about $10,000 on her with all the problems (these are in 1998-ish dollars).
My cat is smarter than your honor student.
Stop Dog Fighting ~ Neuter Mike Vick!
~ RIP Timmy ~ May 2009 - November 6th 2009