OP, here are a couple of tips for giving pills or liquid that have worked for me.
If I’m giving a liquid, I squirt it in the side of the cat’s mouth. That is, I insert the syringe at the back corner of his lip. I find it often helps if I scruff the cat and hold him up so that the front legs are in the air. The trick is to be quick–pick him up and dose him before he realizes what just happened.
For pills, I like to use a pill dispenser. I open the cat’s mouth (get your vet to show you how if you’re not sure) and place the pill as far back in the mouth as I can. Then I hold the mouth shut and blow lightly on his nose and rub his throat until I see him swallow. Then I chase the pill with about a cc (1 mL) of water just to make sure it goes down.
For metronidazole, I give pills if I can get them down. I also have some liquid on hand so that if the cat spits the pill out and it dissolves, I can still give the liquid and he doesn’t miss any doses.
You can find some good videos on giving cats pills and liquids on YouTube. For both pills and liquids, the faster you work, the better. I hope your cat is a good sport; otherwise you’re going to have a stressful few days.