I think Grant is one of those actors that have believable chemistry with most of his costars. On top of that he has the acting chops to work that skill whether there is a need for a platonic or romantic relationship. At least I can see it being differentiated between different relationship he has on the show.
I do think the strongest one he has with Candice and it's sort of on a undescribable level, it's so organic....with him and Melissa and how they play Barry and Kara when in the scenes together I see this skill of his being utilized on a friendship / siblings level and I like it because its natural and not forced.
And also, I don't SHIP Barry and Kara, I just said I like the sibling like dynamic that they share. Plus I only use SHIP word when it comes to romantic relationships. In all honesty I actually barely use that term....