Jeannine..you can pot your onions up for seed saving..but..larger the pot the better, as providing enough water later on will become issue. As for pot size, well I would look for having couple of inches of spare room/compost around the
the onion when planted...more don't hurt.
Use soil based compost if possible or make mix with grit to add some weight to their root balls. The flower heads are suprisingly heavy and they do tend to topple over...been there.. ::) Even cane pushed through bottom of the pots into soil would not go a miss and that is another good reason have larger pot.
You could try your luck with shrivelled ones...but I'm afraid those would have used their energy for green growth from the bulb instead taking it from the soil..but who knows, nature does throw suprises every day. Maybe 'emergengy' dip would help..soak the bottom of the bulb (the growth plate) in little water with added well diluted nitrogen feed untill roots start developing. When the roots are still short plant the onions, try not to damage the roots. Hopefully the the 'dip' will have chance to plump up the bulb or at least replace some of used up energy from the bulb.
In UK I would start re-planting onions for seed growing around March..or depending how early they start top growth maybe earlier and in pots and under cover. I would time them same as growing from sets..but how that translate into Canada's climate, I'm not sure.
