Before I respond to your specific questions, I should say I get the sense that are not looking through the reference manual, other supporting documents, or previous forum posts before posting. I would strongly recommend trying to help yourself first by carefully reviewing these documents before posting. Otherwise you are wasting your own valuable time waiting on people to respond when the answers are easy to find on your own.
I have tried to put the steady state in the model block in the “#” form, but it says that I can not define more than once the “_ss” variables, so I am not sure which ones to put.
Without a .mod file I can only guess at what you have done. You can not include the “_ss” as variables in the var block and then again as model locals in the model block. See Listing 3 in A Guide to Specifying Observation Equations for the
Estimation of DSGE Models and the discussion surrounding it for an example of proper implementation of this approach.
I am trying to replicate a 2001 paper An Estimated Canadian DSGE Model with.pdf (236.8 KB), but I have certain problems trying to state that the estimation must be done by maximum-likelihood.
I do not know what “certain problems” means. In general to estimate using ML you just choose the appropriate mode compute algorithm, as outlined in the Dynare documentation on Estimation.