“I can” starts off limited, you must still choose to do what has been presented to you.
“I will” hits the ground running and gets results.
Philemon v21 “Having confidence in thy obedience I wrote unto thee, knowing that thou wilt also do more than I say.”
Paul knew his friend Philemon so well he knew that he would not only do what was asked of him but that he would go above and beyond, hence the part “knowing that thou wilt” wilt or will same thing.
When God gives us an assignment is it a matter of “I will” or “I can”?