This should be easy.
In the BFD UI Mixer page, at the bottom of the screen there's a dropdown which shows where each track is currently routed to. It'll say something like "Master", "Aux 1" etc.
I would start by assigning your kick to Mono 1, Snare to Mono 2, Hat to Mono 3 etc
Route your Overheads to Stereo 2, Room to Stereo 3, Am3 to Stereo 4 (You can't use Stereo 1 - this is reserved for BFD's Master out)
Then, in Sonar, if you've already got your audio tracks mapped out, just change the Input of the Kick to BFD Left Mono 1, Snare to Right Mono 2 etc.
Make sure the interleaves are all mono apart from OH/Room/Amb3
OH/Room/Amb will go to Stereo tracks, not mono
That's about it.