quantizing a whole song

I’m using Cubase 3. I have two ~7 minute tracks, and I would like to mix them like a DJ would. One of them has a fixed BPM, 126.9, call it track A. The other one, track B, is live piano. There is a 4/4 rhythm and it varies between 124 and 128 BPM. I can easily tap the four beats in a measure. There are no clear attacks in the waveform.

I would like to mix these two tracks together at 128 BPM, preferably without noticeable loss in audio quality. Is this possible? Is there a step-by-step guide? In an ideal situation, I would simply specify the number of measures in A and adjust the tempo. For B, I would tap four notes to a measure, adjust my tapping, and quantize.

I tried playing with warping, but didn’t get anywhere useful, certainly nowhere near a workflow that I could repeat and apply to the entire song. Video tutorials, etc. are wonderful. I thought about recording a separate tap track while listening to B so that I knew where to put warp points in B afterwards. Is that the best way to go?

Thanks, I really appreciate it.