It all depends what kind of gap you have between Good Boo, Pure Boo/SS3 Goku and Base Gotenks (post). Imo, Goku shouldn't have too much trouble here, unless he gets hit by the Kamikaze Ghost.
Base Gotenks > Base Goku >> SSj3 Goku (Boo) imo
Goku SSj3:480
-EoZ Base:2
Base Gotenks:2.4
with that and my Big SSj2 Multiplier , Goku would win unless Gotenks hits him with Kamikaze Ghost
Yeah. you would need to have a 5x SSJ2 multiplier in order to make this fight even in my opinion. I can barely even see the multiplier being 3x, let alone 5.
Imo, Gotenks is a tiny bit stronger, and has some dangerous attacks up his sleeve that can win this for him. But Goku is the better fighter, and has much more battle experience as well as some deadly combos (e.g. Instant Transmission + Kamehameha).