In the first episode of Stargate: SG-1, it is implied that MacGyver is a TV show in the Stargate universe, when Samantha Carter comments on the compactness of the DHD, and how it "took them years to MacGyver a system [emphasis mine]" on Earth.
If this is the case, what actor is likely to be portraying MacGyver, as Richard Dean Anderson probably doesn't exist?
(Caveat 1: This answer probably does not have a canonical answer.)
(Caveat 2: The canonicity of the existence of the MacGyver TV show in-universe is possibly dubious, as the recut of the first episode, "Children of the Gods", omits the line entirely, and no further (spoken) references are made to the show.)
(Caveat 3: It is of course possible that Richard Dean Anderson does exist in the Stargate 'verse, in a Rainier Wolfcastle type situation.)