The point is to get a tax deduction for interest expenses that are currently not tax-deductible. This is a fairly routine step that most accountants would suggest. Why wouldn't you take the deduction? Also - there are no significant costs involved in set-up as long as 'interest penalty' for breaking existing mortgage is not involved.
Legal fee is minimal (<$1000)
Mortgage interest (not a factor since OP is already paying that)
Capital gains (not a significant factor as OP stated is ACB is close to market) - on the contrary he may be able to utilize previous losses that he may have had because of deemed disposition (his move from US).
Now the benefits:
OP's marginal rate is 47.97% in Ontario (46.41% for spouse). Assuming OP and spouse are paying $11,858 in interest expense ($484K X 2.45%), together they will save $5,597 per year in taxes. A small amount for OP but the point is that they are not getting this right now. The one-time costs will be nowhere near this amount.
There are many variations that may be used as long as they involve some tax planning.
Even if I had $20 million in bank - I would still be doing this.