a few current numbers that may help, because the schedule has moved since September and some figures earlier in this thread are now wrong in both directions.
First, the duty follows where the goods were made, not where they ship from. China-made fitness equipment shipped from Canada to the US takes the China stack.
For 9506.91.00 (gym and exercise equipment) of China origin, the current schedule stacks to 24.6%: the 4.6% base rate, plus 12.5% under heading 9903.05.31, plus 7.5% under 9903.88.15. Both headings are checkable at hts.usitc.gov. The 42% figure from September was right at the time, but 2 of its layers no longer exist: the IEEPA reciprocal duties were struck down in February and the Section 122 surcharge expired on 24 July. So a checkout charging 132% is not reading the current schedule, and a tool still adding last year’s layers will also be wrong, just less dramatically.
For the Canadian-origin sellers here: entering free with a CUSMA claim is correct today. The date to plan for is 19 August. Three proclamations published on 23 July add 50 percentage points to 554 Canadian-origin tariff lines from that morning, and qualifying under CUSMA does not exempt them. 9506.91.00 is on that list, and so are the main jewellery lines in chapter 71. Anything assuming the agreement still zeroes those lines on the 19th will underquote.
On the 100% on 3304.99: I cannot find a route to 100% for that line in the current schedule for the origins mentioned in this thread, which suggests a fallback value rather than a calculation. Worth giving support the expected stack for your origin rather than the symptom.
I build a Shopify app that re-verifies these rates against the published schedule twice a day, which is the only reason I have current numbers to hand. Happy to work through any specific code and origin if that helps.