Use an aged domain or a new keyword rich domain for SEO?

It's no secret that Google put more trust in sites and domains that are aged, if you had asked the same question 1-2 years ago then I would of told you pianotuningtoronto.ca however times have changed and Google cares little for EMD 'Exact Match Domains', so there is little to no benefit in actually using keywords in the domain name. So while both are valid domains since the shorter domain is aged your customer should opt to carry on using the domain that is trusted by Google, rather than starting all over again to gain Google's authority and trust. (site moving using web master tools does not pass all trust across).

Your customer should opt to target keywords in the url paths rather than the domains.

So for example:

ivories.ca/piano-tuning-services-in-toronto/
ivories.ca/piano-repairs/
ivories.ca/parts-for-pianos/

Also its worth mentioning that pianotuningtoronto doesn't look like a company name but rather than a service, your client cares about business image/branding even more reason to stick with using Ivories.