Answers....
Hi!
Stargate is filmed and produced at Bridge Studios in Burnaby, B.C., which is a suburb/neighbour city to Vancouver. The outdoor location filming is done in the nearby Seymour Mountain, Richmond (the sand pit-like scenes), public parks, downtown Vancouver, Vancouver buildings, the beach (eg Fire and Water in Season 1).
Peter Williams is originally from Jamaica. At Gatecon he affected a Jamaican accent. But he is part of the Vancouver and Canadian pool of actors. He has appeared in other shows filmed in Vancouver and Canada.