The thing is Karlovic only hit 53% of his first serves in against Chardy who was absolutely nailing the second serve returns. Isner will probably serve at 70% at least and he's tougher mentally than Ivo so I'm unsure of this.
Isner is injured & physically dead, Chardy mentality can be similar to someone like Kyrgios though re: getting broken through mental lapses against bots... I'll go with Chardy in a final set TB when Isner is completely done physically
^ You don't know your country very well, i've been living in Monreal for 3 years and not only do they speak french here, but there is also a lot of french expats in Quebec. Chardy will have the support of the crowd.