Both are very good Pokemon to choose from, and their both incredible sweepers. But, in my opinion, I would lean more towards:
Arcanine > Electivire
The reason behind this is their overall structure on how they attack.
You're looking for a physical sweeper. Right off the bat, you would choose Electivire, since he has much more. But, Arcanine is behind by a close second. To find great physical moves, you need to look at their moveset. Elective has a wider range of his move set, but the lack of special attack took away a lot of great and powerful moves such as Thunderbolt - some of his higher STAB attacking moves. Electivire doesn't learn much physical moves as Arcanine. Therefore, Arcanine would be a much better choice. Approximately 90% of Arcanine's moves are physical. So, you can find lots of incredible moves to support him and make him a great Pokemon.
Many people (sometimes me) would choose Elective because he's the more powerful Pokemon when dealing with attack, and he can be used incredibly. But, in this case, Arcanine would be the better teammate. Elective may have more resistances, but the balance between weaknesses and resistances for arcanine, make him the better choice. Also, Arcanine does have a better base stat total, and having an average stat range helps a lot with attacking and find great Pokemon; also seeing that his is higher.
Normally, I would love to choice Electivire for the last spot on my team, but I pretty sure that Arcanine would be the better, and more ideal Pokemon for you. He also might be a little easier to recieve, depending on what game you're playing. Hope I helped! :)
