Kuobin,
The FAA AIM states that, "e. A visual approach is not an IAP and therefore has no missed approach segment. If a go around is necessary for any reason, aircraft operating at controlled airports will be issued an appropriate advisory/clearance/instruction by the tower. At uncontrolled airports, aircraft are expected to remain clear of clouds and complete a landing as soon as possible. If a landing cannot be accomplished, the aircraft is expected to remain clear of clouds and contact ATC as soon as possible for further clearance. Separation from other IFR aircraft will be maintained under these circumstances."
The Canadian AIM states virtually the same thing. No altitude is specified other than to follow ATC instructions at a controlled airport and to remain clear of cloud at an uncontrolled one.
As mentioned above some published missed approaches do have missed approach procedures to follow, but the are nonetheless not an IAP.
best regards,
Bruce Waddington