As a general rule, CRA will not accept less than the full amount owed when dealing with an individual taxpayer. The CRA logic is simple: if they allow you to pay less than the full amount owed, they may be forced to make the same deal with everyone else.
It is possible to settle your tax debt for less than the full assessment amount, both principle and interest. The reduced amount that the CRA is willing to accept depends on your individual circumstances, i.e. your income and what assets you may own.
And as was described above, there are taxpayer relief provisions used by the CRA, and the CRA can cancel or waive interest or penalties under certain circumstances.