The Executive committee chooses the chair so just make sure you have enough members on the EC who support your nominee.
By the way, the correct process is that the meeting decides how many members the EC should have (maximum 9) and then the EC holds a meeting after the AGM to elect office-bearers.
The strata manager can’t use proxies to elect him or herself on to the EC.
One person can fill all three roles – chair, secretary and treasurer – if that’s what the committee wants.