Though here in this sentence Mainu can be used but it will sound unfamiliar to a native speaker's ear. They mean the same but can't be used interchangeably across the board. A linguistic can tell you more about this. Mainu aje gaddi chalauni nayin aundi, Mainu ajj gaddi chalani paini hai..in such sentences "Main" can't be use. Main aje tak kadi gaddi nayin chalaee- Mainu can't be used in this construction. Mainu actually stands for 'to me', 'also me, but even this justification won't suffice because Mainu Pata hai ( I know) alone is correct. You can't use "Main" here unless you say "Main eh janana haan"
Main ajē gaḍī calā'uṇī hai.
If you say Mainu in place of Main like Mainu aje gadi chalani hai- it won't be completely wrong as Qureshpor's reply suggests but it is not a very common usage of Mainu in place of Main. Main gaddi chalani hai and Mainu gaddi chalan de or Mainu gaddi chalani aundi hai..these compositions are correct.