Their turnaround in fortunes since their 2015 World Cup disaster has been awkward and a boost for Gatland as he straddled his Wales and Lions portfolios. With the Lions now his sole priority, Gatland will be inspecting the candidates with a singular devotion.
Two England players stand out as they tangle with France who are reputed to be revitalised under new coach Guy Noves.
There are stacks of very talented loose forwards but England's Maro Itoje will get extra attention.
Itoje made his way through the national age grades as a lock where his athletic gifts conquered any thoughts his rivals might have of swamping his 1.95m frame in the lineouts. He carries plenty of sting with his 116kg and with multi-sport success, leadership success and the smarts to read politics at university, Itoje is part of the new wave-England.
He has played lock but is picked on the blindside this weekend which gives England a prized third target in the lineouts. The inspection will be how he deals with his other jobs on defence. But at this stage, Itoje must be in a shadow Lions squad.
Five-eighths George Ford is on the cusp in a heavy battle with other talent including Owen Farrell, the sharp-shooting goal-kicker picked outside him in the England backline.
Ford was at the helm for last year's Six Nations where his ability to stay up in the line and use possession was a change in team structure since he was replaced by Farrell after the opening game in the 2015 RWC.
Ford is only 23 but he's played 30 tests as he's encouraged to explore his instincts with the possession England's forwards can deliver. The tactic worked last year but international rugby is an unrelenting inquiry and that's where the Lions have to be certain of their men.