For the Princess Half Marathon (assuming the same course route is used this year as last year) buses from all resorts go to the TTC - NOT the MK bus plaza - until runners are cleared of that section of the course (I was in MK last year when the last runners went by on Main Street, which was about 8:30am).
So depending on your timing, your bus from POR to MK will likely go to the TTC. If so, take the resort monorail around to CR.
A word of advice, build in plenty of extra time that morning. It all depends on your timing and what's going on between points A and B, but it can be slow going getting around certain parts of WDW that morning.