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Generally, this is a sign of an insect infestation. Spider mites, mealy bugs, aphids, thrips, and whiteflies are common pests that affect hibiscus plants, sucking sap from them and resulting in anything from poor growth to leaf curl and drop. Thoroughly inspect the plant to see if this is indeed the problem and then treat the plant with neem oil. If you do not see any signs of pests, check the soil to ensure it is getting adequate moisture.

Lack of flowers can be due to watering issues, pests, not enough sunlight or over fertilizing.

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-fertilizing.htm
https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/how-to-care-for-hibiscus-plants.htm

This article will help you.

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/tips-for-pruning-hibiscus-plants-when-to-prune-hibiscus.htm

Your answer depends on what type of hibiscus you have. Some hibiscus are hardy and some are tropical. Tropical plants usually have very glossy, dark green leaves. If it was located among the perennials at a garden store, then I would assume it is hardy in your region. Browse search engine images for your plant and follow the link to the page that IDs it. Or use a plant ID website and post a picture. Hardy hibiscus will make it through a zone 4 winter which is Carleton Place's zone.

Hibiscus has to go through a cold period to reset the bloom cycle. If you brought the plant indoors and didn't let it go dormant, the bloom cycle hasn't been triggered.

This is very common with Hibiscus plants, so it is not a sign of poor health or that you are doing anything wrong. They will often drop blossoms because of temperature or water stress or the presence of insect pests. You could try providing it with some shade, watering more evenly, and checking for any insects on the plant.

https://www.gardeningknowhow.com/ornamental/flowers/hibiscus/hibiscus-flowers-hibiscus-blossoms-falling-off-plant.htm