Halys is a very tricky player because he has tremendous serving ability, which makes him very hard to beat when he's firing on all cylinders. It hasn't happened often lately, but he had some really good runs in recent years.
Auger-Aliassime played many times at the ATP 250 event in Marseille and made it to the final two times but lost both times. He's always been a fairly decent indoor player and had a good week in Montpellier. He'll look to extend that solid play to this week and there are some good signs he'll be able to do so.
They have never played against each other so far, but there are certainly things we can look at. In most rallies, Auger-Aliassime should have the upper hand because he is the better player, especially with the way his game has been trending so far.
Halys should never be underestimated indoors and on home soil, but unless he can find a really strong serving day, he won't have a very good time in this matchup. His play recently hasn't been inspiring, and it's not about recent form either. He's failed to reach his old level for many months now.
Another thing that needs to be remembered is that he played for France against Taiwan in the Davis Cup on Sunday, and that's a long flight home. It might not affect him that much, but he'd ideally be back home preparing for this event as opposed to that.
Auger-Aliassime was not only in France but also nearby in Montpellier, so he should be better prepared for this. He should also be more confident in his recent level, which certainly adds more merit to backing him here.
Prediction: Felix Auger-Aliassime to win in two sets.