Originally Posted by NewbieRunner

Welcome to FlyerTalk and the Lufthansa/M&M forum, Readingdemon!

You are correct about security and passport control in FRA. Your flight from OSL usually arrives at an A gate or A bus gate, and the YYZ flight departs from a B gate. When you arrive in A following the signs for B gates should take you to an elevator between gates A15 and A17. Go down the elevator, walk through the tunnel, go up another elevator at the end, turn right and go through passport control into non-Schengen B departures.

I’m not sure if it’s worth paying for a seat near the front but it may be a small price to pay for peace of mind.