Mirrorless vs DSLR upgrade

[NoviceMom2Boys]

Looking into upgrading my 15+ year old Canon Rebel Ti…to either a newer DSLR or a mirrorless. Mostly shoot in low lights for events, and sport action shots-mostly outdoor but many @ night. I have a Sigma AP070-200 mm lens…I would love for the new camera to be compatible with the lens (it is about 7 years old). I have heard mirrorless vs DSLR is mostly a preference of photographers, I am not a photographer but enjoy taking shots at special events and sporting events. I have used one of the newer Sony mirrorless cameras and the quality of the picture and color was amazing without any editing necessary, I would love to stick with Canon because the Rebel has been an awesome camera, however, it is beginning to show its age compared to new models and their capabilities. 

[Waddizzle]

I would recommend a mirrorless, MILC, camera body.  The selection and availability of new DSLR lenses is dwindling.  In the case of Canon lenses for the EF mount, you will be mostly looking at the used lens market.

Also, many DSLRs are reaching their end of the service life from Canon Repair Centers.  The.   Typical service life in the US markets has been 7 to 10 years for most Canon DSLRs.

If I know your budget, then I’d suggest an R50 or R100 camera kit.  Add a Canon EF-RF mount adapter to the package.  The first place I’d look would be the Canon USA Online Refurbished Store.  Both were on sale over the holiday season.  They may go in or out of stock without notice.

https://www.usa.canon.com/shop/p/refurbished-eos-r50-rf-s18-45mm-f4-5-6-3-is-stm-lens-kit?color=Blac... 

[rs-eos]

Agreed; avoid DSLRs at this point, especially since it seems you keep your gear for a very long time.  You'll get much greater support over the years with Canon's new R-series cameras.

Do note though that there's a chance that your third-party lens won't be completely compatible when using it on such cameras with the EF to RF adapter.

[Tronhard]

It is difficult to give tailored advice without an actual budget figure, so advice is going to possibly stray outside what you are prepared to pay.

The Sigma APO 70-200 is an old design dating back to 2010, so with 14 years under its belt you need to test its functionality with any R-Series MILC, using a Canon EF-RF adapter, before you purchase if you really want to keep it.  An option would be to sell the camera and lens now to release funds and move on from the DSLR platform completely.

However, as my respected associates indicate, you definitely want to move to the R-series MILC platform.  To make the most of the move, both in terms of optical performance and focusing - especially in low light as you indicate - you will need to consider a RF lens.  When you checked out the performance of the Sony, it will likely have had a lens built for that platform and thus you will have seen the performance of a dedicated and integrated system.

Since you shoot in low light, I would personally point in the direction of a full-frame camera rather than a crop-sensor body such as you have as they generally perform better in dim conditions - likely candidates would be the R8 or R6 (or R6MkII) body, which you can get from the Canon Refub store: Canon Refurbished Cameras & Accessories | Canon U.S.A, Inc. 

As to a suitable lens, for roughly the same reach, I would recommend the RF 100-400 IS USM which render images roughly equivalent at the short end and a bit better at the long end, thus surpassing your 70-200 on the crop body also available: Shop Canon Refurbished RF100-400mm F5.6-8 IS USM | Canon U.S.A., Inc.