Canadian income earned and effect on US Social Security

Hello I have a question as follows:

- I am Canadian who has worked in the US for 15 years.  I will be retiring and am eligible for SS benefits. 

- I understand that as I am collecting SS I must complete a US tax return prior to submitting my Canadian tax return.

           Question:  What do I need to claim on the US tax return as income ?  

                                        - as the only "US sourced" income is my Social Security, is this all that I need to claim on

                                           my US tax return as income ?   I assume that I do not need to identify "Canadian                                                       sourced" income such as RRSP income, employment income ?  

 

I assume that "US sourced" income such as SS is taxed in the US and "Canadian sourced" income is taxed in Canada ???  Is this correct ?    Also, a related question, if my assumption is correct and I work full time back in Canada, will employment income earned in Canada affect my Social Security benefit amount ?