The slump likely has little to nothing to do with your switch to CAD.
Canadians recently turned away from shopping online due to the threat of a Canada Post strike/lockout.
My own sales (which have been exclusively in CAD since Jan 2013) are generally steady January through October (rising for Xmas) took a nosedive to about 25 per cent of normal when news about postal labour disruption hit the airwaves and newspapers in earnest in mid-June, and those numbers have not recovered since. It's been about 45 days of little-to-nothing. Lots of unpaids and that's it.
While one could question whether ebay is doing enough to remind shoppers we're still open, the company has done its part urging CPC and CUPW to resolve their differences so that we can continue to earn a living selling online. See http://www.ebaymainstreet.com/news-events/head-ebay-canada-sends-letter-canada-post-postal-union
By all means, come back on Wednesday at Noon EST and raise your concern directly with ebay Canada staff. Join the Weekly Board Hour where eBay Canada staff will be available every Wednesday to answer questions from 1PM - 2PM Eastern. http://community.ebay.ca/t5/Weekly-Chat-Session/bd-p/23000000073