What Sennheiser model do you have? I ask because the higher-end ones (if its from the 565/580/600/650 family specifically) can have their drivers (and basically everything else) replaced for less than the price of replacing the headphones. Just contact Sennheiser's support department to order parts - at least that's what I've always seen done.
Also, what are you plugging these into? Can it handle high impedance loads and/or low sensitivity models?
As far as Sennheiser manufacturing country of origin - as far as I am aware, the 580/600/650 family is still coming from Ireland, the silly expensive models are German made, and the "consumer" stuff like HD 280, 555, etc have been made in China for some time, as are the newer models. I'd be very cautious if you go after the 5x5 or 5x8 series, as many users report cracks in the plastic from use over time (such a great feature in a $150+ product, isn't it? the more expensive models (even the HD 650) can actually have this problem too - they're all plastic after all). Personally I've never liked the sound quality that much to bother with them.
Now, onto headphones themselves: the $100-$300 segment is absolutely flooded right now. Most of it is garbage; sadly (bass-boosted, bloaty, etc to try and latch-on to the "Beats By Dr Dre" phenomenon). My advice would be to look at models/manufacturers that've been around since before the "trendiness" began. Also remember that due to said "trendiness" the $100-$200 segment isn't "high end" anymore (which is also ridiculous, but it is what it is).
Some various models that come to mind (all based on personal experience; feel free to ask any questions you've got - this was/is kind of a side hobby for me):
- Koss MV1 and PRO4/AA. Both are made in the US, both carry the lifetime warranty, offer good isolation, and good construction quality. The differences in sound are not subtle - the MV1 are relatively flat and clean sounding, the PRO4/AA are a bit more "hi-fi" sounding (more bass and treble, but certainly not boomy or bloated). In the US they should be around $80-$100/ea but I don't know if their prices change dramatically in Canada.
- Ultrasone HFI-2400. Made in Taiwan, open-back, very comfortable. They feature Ultrasone's S-Logic functionality (which is not DSP/filter based - it's based on how the drivers are physically arranged in the housing), which takes some getting used to. Sound is more towards "hi-fi" (the HFI line targets that), but will cover a wide frequency range. Last I knew pricing was around $160-$180. There is a higher-cost "pro" version (PRO2900) which do improve pretty much on all aspects, but they cost more like $550.
- Grado SR series (aka Grado Prestige series); SR-60 through SR-225 fit into your budget and would all be good choices. All made in the US, and all have good service/support behind them. They're open-back and quasi-on-ear (depends on how big your ears/head is); some folks have complaints about comfort and isolation, others don't. Make sure you go through an authorized dealer or Grado won't support them/you. The Alessandro models are built by Grado and based off of these parts - both sides are pretty mum as to what the real differences are.
- AKG K701 (and its millions of variants). Very comfortable, very light, very spacious sounding headphone. Relatively flat (not the bassiest thing ever though), somewhat insensitive (needs more power than the average headphone, but nothing outrageous - we're talking 1-2 mW vs .1-.5 mW). The original 701 was made in Austria, I'm not sure about all the variants (check whichever variant you end up picking - the biggest differences are the color and if Quincy Jones is hawking them).
That's the whatever half-dozen that come to mind off hand; there's certainly others I may think of, and feel free to ask about whatever model/spec/etc comes to mind (there's a reasonable chance I own, have owned, or have spent time with it - as long as it isn't a "trendy" model).
Oh, on the "cables must be detachable and replacable" - those things aren't mutually inclusive. For example many Audio-Technica headphones do not have removable cables, but AT will sell you a complete replacement harness that you can install yourself (or pay a bit to have ATUS Support install). Same is true of Koss and Grado - although in both cases it has to go back to the manufacturer (Koss doesn't charge, period; Grado I think charges for parts if its out of warranty). Also keep in mind that for most headphones with removable cables, they use a proprietary connector (which in some cases is a point of failure in and of itself (looking at Sennheiser on this one)), and the replacement cables are usually silly expensive ($50-$100; yes even on a part that costs $50-$100) because they're only available from the manufacturer.