He looks to me like Collie/Border Collie mix.

The structure of his body in the pics and how he holds himself say Collie although I don't know anything about BC's. His markings are that of a Collie and the way his tail appears to be "low slung" say Collie to me. His face looks Border Collie and his ear set looks B/C. And his weight is about that of a BC. Male Collie's are much larger than 45lbs unless they just come from EXTREMELY small parents. But again BC's are around this size aren't they? But I don't think Sheltie at all but of course I don't know his personality either.
Collie/BC is my opinion