If you have not been explicitly asked to upload your marriage certificate under the IMM 5409 line, then you do not need to upload it there. However, you should ensure that you have uploaded all relevant documents related to your change in marital status. This may include your marriage certificate, if you have not already provided it to IRCC.
Also if there is an additional document link you can most likely add it to that, I am unsure of this process as I have not done it myself, if you feel like you want to provide additional documents you can also upload that in a webform to IRCC and explain why you are sending it that way and ask them to add it to your file just to be safe, even though they will likely tell you to not send doc they did not ask for but will not hurt to. hope someone else provide a better reply if they had same issues
Good luck.