Audiosnap, Tempo Map Quantize for project recorded on another DAW

If the project was recorded to a click in another DAW, you should be able match that DAW's tempo and call it a day.
 
If it wasn't recorded to a click, my preference would be to manually set the minimum necessary number of points using Set Measure/Beat At Now to capture the ebb and flow of the tempo of a given piece with tempo changes that SONAR calculates and inserts for you at the points you set. If it's a solo performance with a lot of rubato, you might have to set points within measures, but a typical ensemble performance should be tight enough that you only need to set every 4-8 measures. Then, regardless of how variable the tempo is, so long as it was deliberate, I would not mess with quantizing the audio but would instead use the variable tempo map and click to lay down any new material in sync with the natural timing of the original performance.
 
But if you really want to quantize the original material at that point, you would just enable Autostretch on the audio, and delete the tempo changes.
 
Check this previous post of mine for a few more details:   http://forum.cakewalk.com/FindPost/2922802
 
 

Vlar
What would be the best way to set and trim a one or two measure lead-in with the minimum instance of out-of-bounds tempos or other anomalies?

 
That might depend on what's in it, but if it has any kind of musical rhythm to it at all, you should be able to set all the points without errors so long as you correctly identify which transients go where, and "slide and pin" the first transient in the clip to the correct beat location as described in steps 1 and 2 of the other post. And, yes, it's a good idea to trim and bounce any dead air from the front of the clip so you have full flexibility to position the first transient in the timeline.
 
In cases where the clip doesn't start at 1:01:000 and the initial clip tempo is wildly different from the project tempo you started with, you might want to undo the first couple "Sets" after checking what initial tempo was set by SONAR in the Tempo view, change the tempo of the project to match that initial clip tempo, and start over.
 
If you want to post an example clip somewhere, I can tell you how I would handle it.