Is the backing track "mastered" (read compressed to death, and the waveform looks like a line of toothpaste instead of a waveform)?
Because if it is, it's going to be really hard to sound "in the mix", since there is no headroom left
If there is headroom though, I would just process my vocals the normal way (whatever fits the song... usually some EQ, a compressor, and some form of verb), with effects on the track, and/or reverb on a vocal buss..
I would then add a very slight amount of compression (the most transparent one you have), or veeery short reverb to "glue" the vocals and the backing track together.
I'd slap that on the master bus, but you can also make a folder and slap it on there..
hope this helps