tax implications of holding..

There wouldn't be any tax consequences.
In practice most of us who buy and sell would own two properties at the same time, and in most cases you would reside in your new residence by the time you have closed on the old one, in some cases it would be couple of days, in others couple of months, and I have never heard of any cases where anyone was faced with tax consequences. Don't know if cra has implemented time limit in such cases.
For cra the proving the intent is a major factor, if your intention was not holding on to an empty property but selling it around the time of the move I don't see any issue. If you wanted to get technical you could argue that there is a possibility of a difference between deemed disposition (when you change the residency), or fair market value at the time of the move, and actual selling price 6 months later. Most would simply declare the sale when it happens.

If you're eligible to claim moving expenses, the costs to maintain your previous residence until its sale can be claimed (up to $5000)

http://www.taxtips.ca/filing/movingexpenses.htm

just in case ... if CRA has questions to ask ...

Keep all your docs in order, with the current house listing for sale, who is your agent/broker, date of listing, pics of your house (if necessary for filing). This is just to prove your principal residence is up for sale and you have bought and moved into your next new principal residence

Your gains stay tax free upto a year after you move:
https://www.canada.ca/en/revenue-agency ... tml#N103EF

2.20 The first amount by which the taxpayer’s gain otherwise determined is reduced under paragraph 40(2)(b) is calculated by using the following formula:

A × (B ÷ C)

The variables in the above formula are as follows:

A is the taxpayer’s gain otherwise determined, as described above.

B is 1 + the number of tax years ending after the acquisition date for which the property was the taxpayer’s principal residence and during which he or she was resident in Canada. (Note that both these conditions must be satisfied for a particular year in order for that year to qualify for inclusion in variable B.)

C is the number of tax years ending after the acquisition date during which the taxpayer owned the property (whether jointly with another person or otherwise – see ¶2.9).