Here's a snippet. Rest at link above.
“Going way, way back, I was actually up for Michael Shanks’ role in the original series,” Smith explains, speaking, rather ironically, from a seat inside the disused Stargate SG-1 gateroom set. “So I knew some of the producers, and particularly Richard Dean Anderson’s partner Michael Greenburg. He was always looking for a way to get me on the show.”
Smith had a bit of a wait before that happened – seven years, in fact, until an episode of Stargate SG-1 entitled “Enemy Mine”, appeared which called for a geologist named… Evan Lorne.
Thank goodness they didn't go with the geologist role!