Man, that sucks about your mount. I've been there and it's honestly the worst timing right before a wedding. Unfortunately, the preamps on the 90D are just okay and they really hiss if you don't feed them a hot enough signal... been frustrated by that more than once. To get a clean sound you really need a mic with a built-in gain boost to bypass the camera's internal junk.

• Rode VideoMic NTG On-Camera Shotgun Microphone: This is my go-to now. It has an internal preamp so you can keep the camera gain super low. I had issues with older Rode models being too noisy, but this one is way cleaner.
• Deity V-Mic D3 Pro Super-Cardioid Shotgun Microphone: Solid alternative. The stepless gain knob is perfect for dialling out that 90D noise floor. It feels a bit less sturdy than the Rode tho. You definitely need something with its own power to avoid that internal hiss. If you are in London, you should be able to grab both at a local pro shop before Friday. Let me know if you need help with the menu settings to fix those levels!

@Reply #1 - good point! Honestly, the 90D preamps can be a real pain if you arent careful with the gain staging. I've been shooting with that exact setup and I'm really happy with the Rode VideoMic NTG On-camera Shotgun Microphone. It has a dedicated gain knob on the back which is basically a game changer for the 90D. You can dial the cameras internal recording level way down to like one or two clicks above zero, and then use the mics own preamp to boost the signal. It kills that annoying hiss you mentioned. If you want something a bit more compact for running around a wedding venue, I am also quite satisfied with the <a href=" https://www.bhphotovideo.com/c/search?Ntt= Sennheiser+MKE+400+Compact+Shotgun+Microphone&BI=8941&KBID=10361&SID=2222&DFF=d50" target="_blank" rel="nofollow sponsored">Sennheiser MKE 400 Compact Shotgun Microphone. It fits right in your budget and the build quality is solid enough to survive some bumps. It has a built-in wind shield too which is nice if the London weather decides to get breezy during the outdoor photos. Both of these should get you through the wedding with much cleaner audio than your backup cheapo mic. Since you need it by Friday, most shops should have these in stock for quick shipping. Definitely give the Rode a look first tho, that gain dial is just too useful for Canon bodies. Good luck with the shoot, weddings are stressful but you'll do great! If you need help with the menu settings just shout.

To kill that 90D hiss for your wedding shoot, heres what works:

• Get the <a href=" https://www.bhphotovideo.com/c/search?Ntt= Sennheiser+MKE+400+Directional+On-Camera+Microphone&BI=8941&KBID=10361&SID=2222&DFF=d50" target="_blank" rel="nofollow sponsored">Sennheiser MKE 400 Directional On-Camera Microphone. Use its +20dB boost switch and keep your camera gain at the lowest possible manual setting.
• Avoid auto-gain at all costs or itll hiss like crazy during the vows.
• Its well within your 200 budget and is super reliable tho... maybe grab a windjammer too.