Question

i wish you ______ tell me earliest ( can /could/may)​

Answer 1

I wish you could tell me earliest.

Answer 2

Could

I wish you could tell me at the earliest

Could is the past tense of can and can be used in the reference of a possibility (They could win), as an ability (She could eat only a few things), as a request (Could you lend me the pen please?) or as a request (Could I drop you off?)