Planting blueberries in pots is just a bad idea if you can avoid it, the roots dry out too fast and too often and blueberries hate that. Some plants like a deep watering with periods to dry out in between so the roots don’t rot, not blueberries, don’t let the roots dry out.
Blueberries planted in the ground have shallow roots. Keep the base of the plants mounded with compost or bark dust, regular sawdust or wood chips work too. This keeps the roots protected from drying out in the summer and freezing in the winter. It also helps to acidify the soil.
Planting a couple different varieties helps increase fruit yield and will extend your harvest time since some ripen early and some ripen later. Water with a soluble fertilizer designed for acid loving plants like rhododendron and azalea. Miracle Grow makes an acid loving blend for these flowering plants that works great. Look on the box and it will also mention blueberries.
I have six mature plants of three different varieties and I will harvest berries starting in July and continuing all summer long. The plants are now 5 to 6 feet high and as large around and it looks like another bumper crop this year. NW Oregon has a great climate for berries. I picked about 20 large one gallon zip-lock bags of berries last year and the plants are loaded with green berries now and bending over.
I give away blueberries like some people give away zucchini.
We currently have 3 and 4 yr old Elliot and Bluecrop growing in 5 gallon containers. We use Canadian Peat Moss which is naturally acidic. We bury them in the 5 gallon container in the ground low enough to allow mulching and protect from the winter cold. They are thriving. We drill holes in the bottom of the containers for drainage. Once our planting area is prepped (takes about a year), the plants are transplanted. Blueberry plants love moist soil, but not standing water.
Huh? You think Edmonton has an extreme northern climate?
How would you rate Peace River? High Level?
And the Northwest Territories,Yukon and Nunavut?
Generally, for potted plants:
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Make sure you are using a potting mix and not garden soil. If you were using the fabric type pots, such as Smart Pots, soil is ok. But for “normal” pots of plastic, ceramic, etc. you need to use potting mix. I think you probably know that already, but it’s a mistake I made when I was a new gardener.
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Make sure the pot drains well. Ideally there should be holes in the bottom for water to drain out. You don’t want the plant in standing water or spending days in soggy potting mix. I know that terra cotta planters “weep”, but I don’t know if they weep enough to keep plants from sitting in swamp-like conditions. On the other hand, I’ve seen people grow successfully with terra cotta planters, so I imagine they may not require special consideration.
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Fertilize regularly. Unlike soil, potting mix doesn’t have the nutrients that plants need, and any nutrients get washed out quickly with regular waterings. I would use a water soluble, quick acting fertilizer and follow the package directions for indoor plants - once every week or two (check directions for frequency).
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I don’t normally use slow-acting, organic type fertilizers for potted plants. It takes a long time for them to break down. Plus, potting mix doesn’t have the food soil web that’s required to break them down and make them available to the plant.
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Don’t overwater. Stick your finger down a few inches into the potting mix around the plant. If it’s damp, don’t water. If it’s getting on the dry side, then water.
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Make sure the pot is big enough to support the growing needs of the plant. I don’t know what size pot blueberries need, but some plants need a lot of room in order to thrive.
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Blueberries like acidic soil. It’s something you may want to consider, but I think the problem is more fundamental than that right now.
You probably know all this already, but I’m just giving a basic checklist.
Blueberries also need a certain number of chill hours each year, where the temps fall below 45F. Varieties developed for warmer climates need anywhere from 150-800 chill hours per year. If you know the variety you can look up the requirements. In other words, I hope you’re not bringing the plant into the house over the winter. 
Generally, I agree with other posters about buying “body bags” from box stores. I’ve had a few successes, but even if the plants survive, those stores don’t always sell the right variety for the climate. You are better off going to a local nursery. Even though there are some not-very-knowledgeable local nursery staff, you have a good chance of getting something that is suitable for your climate and growing season.