An attorney can assist you in preparing a response to CIC, but you can also do that yourself. Bottom line, if the officer has doubts you need to assuage those doubts - provide evidence that the sponsor is living in Canada. A lease or mortgage, evidence of daily living activities, such as bank statements showing debit charges for coffee at Tim Horton's (for example), evidence that the sponsor has used heath care services, etc. If the sponsor belongs to a gym, a log of gym attendance If the sponsor checks out library books, a printout showing recent checkouts. If the sponsor is working, paystubs along with a letter from the employer stating that the sponsor is employed at a specific location inside Canada would be good as well. And so forth - anything that demonstrates the sponsor is in the country.
When CIC has doubts, the best strategy is to provide them with evidence to assuage those doubts. Remember, an officer's decision can be overturned if it isn't a reasonable outcome based upon the evidence - so give them so much evidence that they'd look like asses to refuse on those grounds.
