It is bad enough to receive a notice of assessment from the Canada Revenue Agency (CRA) or the Ontario Ministry of Revenue or the Canada Border Services Agency (CBSA) or some other tax authority. You clearly did not want to be in a position that you have to pay an amount of money (especially large assessments) to the government. However, ignoring the notice of assessment is not the right option to choose concerning what to do next.
If you do not agree with the amount stated on the notice of assessment as the amount (or the imposition of a penalty amount or the interest calculation) or the basis for the assessment or do not know why you received the assessment and want to have the taxing authority make a correction, you usually must file a notice of objection/notice of appeal/request for redetermination or take a positive step to request further consideration of the matter. In almost every taxing statute, there are statutory time periods (also called "limitation periods") which are often 30 or 90 or 180 days depending on the tax at issue and the legal route to resolve the dispute. If you throw the notice of assessment in a drawer, you may miss the filing deadline and lose your opportunity to file a notice of objection, appeal or request for a redetermination. This would be bad for you.
Some tax statutes allow for you to ask the head of the taxing authority or a court or tribunal for an extension of time to file the notice of objection, appeal or request for a redetermination. However, usually you must make the request within the statutory time period for the objection/appeal/redetermination. For example, if you have a 90 day period to file a notice of objection, you must ask for your extension of time before the 90 day period expires. You must explain the reason for needing an extension of time - and saying that you forgot about the notice of assessment is not a good excuse. You must also demonstrate that you intended to file an objection/appeal/redetermination - and saying that you threw the notice of assessment in a drawer shows that you planned to ignore it.
Pulling the notice of assessment out of the drawer one week or one day before the statutory objection/appeal/redetermination deadline is problematic as you will have to find someone to help you file your objection/appeal/redetermination under extreme stress and you will forget important facts and potentially winning arguments. You will reduce your likelihood of success when you do not leave yourself and your advisors enough time to do a good job.
Finally, I hear from many clients who pull the notice of objection out of the drawer years after the limitation period for filing an objection/appeal/redetermination has expired. At that point in time, they are being pursued by the collections department of the taxing authority and the amount of interest after time can double the liability. At some time, it will catch up with you. When you are pursued by collections officers or receive a director's liability assessment for the original assessment amount plus interest compounded daily at 6% or more, you will wish that you did not thrown the original assessment in a drawer. At that stage, there is even less a professional can do to correct any mistakes made by the auditor.