And Townsend, who starred for the victorious 1997 Lions and now coaches the pair at Glasgow Warriors, sites the example of fellow Scot Tom Smith as a reason to believe that a starting spot in the three-Test series with the Qantas Wallabies is well within their reach.
"Everybody on that tour bar Sam Warburton won't know whether they're starting a Test or not," Townsend told The Courier.
"They all have to grab that opportunity and work hard to get in that team.
"Tom Smith played six Lions Tests in a row, but he had just three Scotland caps going into his first tour in 1997. Most people would have thought he'd be behind (Graham) Rowntree and (Jason) Leonard but he played all three Tests.
"Sean and Stuart have been picked for their strengths and they've got the ability to start all three Tests for the Lions."
Townsend was obviously delighted to see two of his squad receive the ultimate honour this time last week but he couldn't hide his disappointment after prop forward Ryan Grant missed out.
Grant has impressed repeatedly for Scotland and Glasgow this term but wasn't included in the six-man prop panel chosen to head Down Under.
Townsend himself experienced similar heartbreak the last time the Lions were in Australia, however, and he insists the 27-year-old will bounce back.
"When I got the call in 2001 to say I wasn't selected it was one of the lowest points of my career. The only thing you can do is what you do every day and weekends, that's play rugby," added Townsend.
"It's great that Ryan's in such good form, we've got some big games coming up and there's a Scotland tour this summer, so he can get out there and keep playing at the level he's been playing at.
"It shows how many quality players are competing for a place when guys like Ryan Grant or Kelly Brown miss out.
"If there are any injuries, which is likely on a Lions tour, I'm sure Ryan's one of the first names they'll be thinking about to replace the props."