Slickr is good enough to handle almost all important aspects of canva. Still, Slickr is just a one man app built under 1 month, so there is some drawbacks.
Slickr is mainly meant for hashnode blog covers, In canva, there is not a particular type for hashnode cover, so its messy on canva. Slickr can also handle things in a way canva cannot. Also there are some out-of-the-box features.
Conclusion. Slick is highly recommended if you're hashnode blogger or content creator.