Can go either way really.
Gaara can feint Onoki's Jinton with a clone but Onoki can make Gaara's sand much heavier and less effective.
Only Kishi knows. I'd put my money on Gaara though. He's younger and we all know the drill.
Onoki would have to be grabbing onto Gaara in order to slow down his sand and he has no way of bypassing The Sand shield. Jinton is too slow and Gaara is versatile enough to dodge any attack onoki has.
Gaara takes this mid diff. He will have some difficulty actually trapping Onoki, making sand is no problem for Gaara even in this battle field as shown in Kimmi fight