Canu assembly not making a single consensus? I've downloaded reads from this BioProject. Using canu with default parameters (no correction), I've got 4 contigs, none of which really look like the reference plasmid here.

The command I used was:

canu -p ip40a -d ip40a_assembly -useGrid=false -maxThreads=6 -genomeSize=175k -nanopore-raw reads.fastq


Granted, the original publication for this sequence used minimap/miniasm but my questions are:

A. Why do I get multiple contigs? Doesn't canu generate a single assembled sequence?

B. This is a plasmid but canu says suggestedCircular=false. What's going on here?
Looking that the link you provided only 30% of the reads appear to be e. coli.  I would suggest filtering the reads for those that align to e. coli and see where that gets you.  Did the original publication describe the method they used for data cleaning? 

A: 

https://trace.ncbi.nlm.nih.gov/Traces/sra/sra.cgi?run=SRR3385327

Unidentified reads: 68.82%
Identified reads: 31.18%
cellular organisms: 30%
Bacteria: 30%
Proteobacteria: 28.09%
Gammaproteobacteria: 19.7%
Enterobacterales: 13.3%
Enterobacteriaceae: 12.54%
Vibrionales: 0.01%
Viruses: 1.17%


B: 

Without a good assembly canu won't be able to determine if the assembled genome is circular.  I would ignore this until you have a good example.