If you show competence and drive, and express interest in PLQ you *should* stand a decent chance. It's easier still if you can make yourself available outside the summer when most reservists do the course. PLQs are constantly running year round. There is no such thing as a reg force PLQ or a reserve PLQ; same course. In practise a few summer sessions will be nearly all reservists, because they are prioritized for that purpose, and the fall-winter-spring sessions are mostly regular force. However if a reserve member is available during the rest of the year, absolutely nothing precludes their unit from nominating them. There were a few PLQ Infantry sessions in the last few years that I got guys loaded on where they were pretty much the only reservists on the course, and typically they did just fine. If your unit is switched on and knows they can do this, and if you show drive and make yourself available, PLQ can be pretty easy to get. If you simply wait in line and only are available for the summer sessions, you'll typically be competing against more people for fewer spots.
Some employers are sympathetic to taking leave without pay for military stuff, others aren't. The nice thing about PLQ is it's one of the easier courses to wordsmith into what it gives back to an employer- leadership and management skilsl are something everyone likes to see.