I am assuming you mean for the Regular Force.
No one can tell you absolutely how many spaces there are going to be. It depends on attrition rates, plans for changes to manning within the trade or that affect the trade, capabilities of the recruiting system to process trainees in basic and basic infantry training, and priorities between trades for allocation of space. This will also be adjusted by how many spaces are filled by direct entry candidates from the Reserves (Component Transfers).
I know one of the Training Centre, of three that teach the basic infantry courses, was averaging about 6 platoons of 30-40 soldiers per year, but with prioritization and staffing they could do more if needed. So if that average holds, with three Reg Force regiments, it means about 600-750 (the math is rough) soldiers per year starting basic infantry training. With 2/3 to 3/4 getting to the battalion with attrition in training.
And that number is just that, only a number. The chance of any one candidate being chosen is also affected by how many active files are in the systemn that he/she is competeing against for each selection board. There's really no way to reverse engineer and 'beat" the system, there are too many variables.