It is possible to get to GM by cannon rushing.
If you want to know how, just checkout the Printf’s channel: https://www.twitch.tv/quasarprintf/v/63725910
He is always going cannon rush: on any map and against any race.
Overall strategies are:
- Vs protoss: go for a straight kill with cannon. Try to kill the nexus.
- Vs zerg: contain (by placing cannons on ramp low or high ground). Prevent the zerg from expanding on his natural or elsewhere. Scout with adepts and prevent drops. In case of drops or nydus, defend base with cannons and MSC. In late game, go either with Robo/staklers or Tempest.
- Vs terran: try to kill the CC with cannons. If the terran tries to fly his CC elsewhere, trap the scvs in by blocking the ramp with 3 pylons.