we'll what size tank do you have
if you wan't fish to live with your pike then a TSN is out they get 4'-5' and would eat your pike long before it grew up TSNs grow much faster then pikes same with aros silver aros are out as well for the same reason black/blue aros are anouther story and adult xingu could live with a black aro for a while but eventually black aros get over 2' around 28'' is common but can get 36'' so may out grow the pike but that would take many years as long as the aro was started small and the pike had some size but not to much aros are fraggile when small
gars could live with your pike as long as they don't get to big i would get a florida or spotted gar they would be the best all the others get really big but for any true gar you need a larger tank atleast 3 feet wide and around 7 feet long would be good for a spotted for life but a 180 2x2x6 could house a spotted /florida for a while but they do get around 3' and need a wide tank or will get a curved spine or panic and smash into the sides of its tank
so it really depends how big of a tank you can get