An unmanageable workload is probably the hardest 'long hours' problem to solve. First try and work out why you have too much to do. One scenario is that you have a ruthless manager. Another is that your organisation, department or team has been overwhelmed with work that couldn't have been anticipated or dealt with in some other way. They will require different approaches.
If you are facing simple exploitation by your boss, you could be in for a rough ride, since the only way to make progress will be to challenge them on it. Acting together with the support of a union if you have one is the most effective way to do this. (If you are not yet a member of a union, you can find an appropriate one on workSMART's Union Finder.) They can, among other things, help you defend your legal working time rights to breaks and rest days, and not to work more than 48 hours a week on average.
If it's a wider organisation problem and your manager is in the same boat as you, you’ll need a different approach, but it is still ultimately your manager's responsibility to keep your workload sensible. Can they get some temporary or permanent extra staff? Can you reorganise the work to do it more efficiently or cut out waste and duplication? Can you postpone less important stuff until it's a bit quieter?
Even if you continue to face a heavy workload, and are prepared to put up with it through loyalty or commitment, are there other adjustments that could be made? It may be easier for some to cope with extra work if they can work more flexible hours. If you are prepared to put in extra commitment, your boss should repay that with extra trust (and perhaps some extra cash or holidays) for you to adjust your hours or working style appropriately.