It’s from 2001 and is archived on the CRTC site, but I found a fascinating document entitled “REPORT ON AM BROADCASTING POSSIBILITIES IN THE GREATER TORONTO AREA.”
 
Essentially it analyzes the open space on the AM band in the Greater Toronto Area at the time, and evaluates which frequencies are open – and whether they’d be of any use to someone wanting to set up a station here.
 
There are also a number of revelations I didn’t know before. For example, Canada has exclusive use of certain frequencies on the so-called X-Band. They are 1610, 1630, 1650, 1670 and 1690. The others – 1620, 1640, 1660 and 1680 - are reserved only for the U.S. Have to admit I wasn't aware of that. 
 
If you’re interested in this kind of thing, it covers a huge range of topics, including what was then called CFYI’s move to AM 640 and projected coverage patterns – positive and negatives - for unused frequencies that could be used in the GTA,
 
Here are a few examples I found eye opening, including the “public relations problem” that would result from blocking off WBEN-AM in Toronto.

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790 kHz
 
This channel was formerly used by CIAO Brampton and Imagineering notes the difficulties associated with operation at the old site, as well as finding an appropriate new site. They note that this channel has some potential as a very small one or 2-tower operation co-sited with an existing Toronto station close to the intended market. I concur that there are too many constraints, both day and night, to rebuild a 5 kW station. However, with the relatively low frequency and Eu, the possibility of serving part of the GTA at reasonable cost exists.
 
940 kHz
 
Imagineering notes that use of this new channel would require relaxation of day-time protection requirements to an adjacent channel allotment in Barrie and night-time protection requirements to CINW Montreal…
 
The new station would wipe out existing reception of WBEN in the GTA. Such reception is, of course, not protected, but loss of it presents a potential public relations problem. Add in the very limited night service, even if the rules are relaxed, and this is not a desirable channel, but I would not rule it out because of the high demand.
 
950 kHz
 
An alternative to using 940 kHz is moving the 950 kHz Barrie allotment to Toronto. (This is long before CKNT took up residence at 960 and that frequency isn’t even mentioned in this report.)
 
There’s lots more as you scroll down the list, including 1280, 1470 and 1480. But my favourite has to be this conclusion about 1580, now home of CKDO from Oshawa.
 
1580 kHz
 
Imagineering notes that use of this new channel would require relaxation of night-time protection requirements to CBJ Chicoutimi QC…Siting needs to be chosen with care to avoid image problems with CFTR on 680 kHz and third adjacent channel problems with 1610 kHz.
 
If it comes down to a choice between 1580 or 1610, the latter offers much better night service and is preferable.

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There is a ton of interesting stuff for people who like this kind of thing and [url=https://www.ic.gc.ca/eic/site/smt-gst.nsf/vwapj/reportamfinal.pdf/$FILE/reportamfinal.pdf]you can read the entire document here[/url].