Hi,
What is the difference between the two?
1. With regards to the meeting next week, who are the participants?
2. Regarding the meeting next week, who are the participants?
The standard expressions are these. There is very little difference.
As regards the meeting . . .
With (or in ) regard to the meeting . . .
Regarding the meeting . . .
Sometimes, these phrases just make the sentence less precise.
You might consider simply saying, 'Who are the participants in the meeting next week?'
Best wishes, Clive