I have similar issue with Magnus. He's ok with the big dogs he knows but with the ones he doesn't, it almost seems like he wants to fight. When I try to turn around and walk the other way, Magnus won't budge. He'll try harder to charge.
A guy I know that trains big dogs says pulling him away when he's in that mode is just fueling him more.
So now I stand in front of him, blocking his view and try to distract him with a treat. Once he calms down, he gets a treat. I get him to sit, stay, and gets another treat. I keep a treat in front of him while letting him watch the other dog and wait for the other dog to be far enough where I know Magnus won't react. Then he gets the praise and the treat.
He haven't fully trained but I'm seeing improvements. I'm just glad he's food driven.