You don't want the Pro Tools way; it's not really stereo. It just considers stereo as two mono signals, which is baked deep into the PT code so I don't see that changing any time soon. While it's fine for set-and-forget applications, if you make changes to the panning, or consider a mix as a performance, it's a PITA to deal with two controls that do essentially the same thing to two mono signals.
The other consideration for a Sonar-specific implementation is what happens with Track View - two strips? Ugh.
What
really needs to happen is applying two different parameters, width and position, to a single stereo signal. Consider the following.
The gray bar is the panpot range. The blue bar represents width, which you would slide within the panpot range. This concept would work for Console or Track view. The pan % would indicate the bar's center in the stereo field (I didn't take the time to change them, sorry).
The gestures could done a several different ways, but my preferred implementation would be click in the panpot and drag up/down to set width, then click and drag left/right to set position in the stereo field.
The downside is that if you wanted to automate width and not just pan, you'd need another automation parameter. But this opens up multiple creative possibilities.
If you didn't want to use a linear panpot but instead use a knob, then a "pie slice" representing width could be superimposed on the panpot knob, and you could move the "slice" left or right in the stereo field by moving the panpot.
This protocol has multiple advantages over the dual mono panpots:
1. Single control takes up less space.
2. Once you set the right width, you don't have to re-adjust it if you change the position.
3. You can "think" in stereo instead of dual mono.
4. More intuitive visual display. Very easy to visualize the position and width in the soundstage.
5. Much better than Pro Tools.